Alternating covalent-ionic and metallic bonding in perovskite borides studied using ab initio methods

Using ab initio calculations, we have studied 20 boron-based perovskites (RM ₃B, where R and M are rare earth and 4d metals, respectively). We show that the coupling between M-R and M-B layers in RM ₃B can be switched from predominantly covalent-ionic to metallic in character by varying the population of the M d shells. Based on the electron density distribution resemblance to the so-called MAX phases [Sun et al., Phys. Rev. B 70, 092102 (2004)], it is reasonable to assume that alternating covalent-ionic and metallic bonding in these compounds may give rise to similar properties as observed for MAX phases.